This invention relates to fiber optic amplifiers that must operate in environments subject to exposure to significant radiation.
Fiber optic amplifiers have been used in various applications, e.g. telecommunication in trans-ocean optical fibers. The principle of signal amplification is based on solid state quantum effects where a high power pump laser beam causes electron population inversion in the fiber energy bands and the stimulated photon emission amplifies the incoming optical signal. To match the energy levels in the optical fiber with pump laser, optical fibers may be doped with rare earth materials, e.g. erbium, ytterbium, etc. The doped rare earth elements generate multiple new energy bands in the glass fiber. The photonic energy from a short wavelength pump laser excites charge carriers and leads to population inversion in the energy levels corresponding to the short wavelength photons. Upon stimulation by an incoming laser that carries data packets, the charge carriers undergo an emission of photons giving rise to amplification of the incoming laser carrying the data packets.
Fibers doped with rare earth elements darken when subjected to significant radiation levels, e.g. outer space, causing degradation of optical amplification and an increase in optical amplifier's noise figure. Although attempts to produce special fibers developed to better tolerate radiation have been made, these special fibers tend to lose their amplification efficiency. There exists a need for an improved way to reduce degradation of rare earth-doped optical fiber due to radiation exposure.